thesis: any point in the whole map should be connected to any other node. In other words: from any point in the whole map one should be able to reach any one of well known points that have to be defined (for performance reasons: at least one point on every continent). This check includes even small islands because ferries are considered to be highways. So it is not necessary to define starting points on every island.

"Floating islands" explanation and issues

Any highways drawn on the map should be accessible by car starting anywhere in the world. Ferries and highways (even railway platforms) are included in "floating islands" check, so almost any island in the sea should be reachable starting from the mainland.

The check works like this: pick some starting highways somewhere around the globe (There are about 100 points picked). Then find all nodes that belong to these ways. Now find other ways that are connected to these nodes. Now find again nodes that are connected to these ways, and so on. The check starts somewhere and travels all roads until there are no more. In the end each highway that has not been visited is marked as a "floating island".

One of the side effects of that is if your country/city/island/... is not connected with the rest of the world, you will get LOTS of such errors apparently without cause. When you fix your connections to the world, most of them will go away (on next update, see above). If you have trouble finding what causes the errors and they don't disappear in a week (maybe somebody fixed it recently, but the map was not updated yet) look on the keepright.at for instructions of contacting the map owner.